One of the hallmarks and driving forces of cancer is genetic instability [Hanahan D and Weinberg R A, Hallmarks of cancer: the next generation. Cell, 2011. 144(5): p. 646-74.]. Specifically in familial cancers, mutations in the breast cancer susceptibility BRCA1 and BRCA2 tumor suppressor genes, key players in homologous recombination (HR), have been associated with an increased risk of developing breast or ovarian cancer [Li X and Heyer W D, Homologous recombination in DNA repair and DNA damage tolerance. Cell Res, 2008. 18(1): p. 99-113.]. It is in this patient population that inhibitors of poly (ADP-ribose) polymerase (PARP) have gained recent attention. PARP family members PARP1 and PARP2 play important roles in DNA replication, transcriptional regulation, and DNA damage repair [Rouleau M, Patel A, Hendzel M J, et al., PARP inhibition: PARP1 and beyond. Nat Rev Cancer, 2010. 10(4): p. 293-301.]. In 2005, two breakthrough Nature papers showed that PARP inhibitors given alone could kill cancer cells with pre-existing DNA repair defects, specifically mutations in BRCA1/2 genes [Bryant H E, Schultz N, Thomas H D, et al., Specific killing of BRCA2-deficient tumours with inhibitors of poly(ADP-ribose) polymerase. Nature, 2005. 434(7035): p. 913-7; Farmer H, McCabe N, Lord C J, et al., Targeting the DNA repair defect in BRCA mutant cells as a therapeutic strategy. Nature, 2005. 434(7035): p. 917-21].
PARP inhibition and mutant BRCA were synthetically lethal in preclinical models, suggesting an elegant, targeted and minimally toxic way to treat patients.
Testing of PARP inhibitors in the clinic has grown exponentially in the past few years. These clinical trials started with using PARP inhibitors as a single-agent or in the combination with another DNA-damaging agent to treat hereditary tumors, and have now moved on to treating many different types of sporadic tumors. Initial excitement with PARP inhibitors came around when olaparib (AZD2281, KU0059436; AstraZeneca/KuDOS) was found to be active in patients with BRCA-deficient breast, ovarian and prostate cancers [Fong P C, Boss D S, Yap T A, et al., Inhibition of poly(ADP-ribose) polymerase in tumors from BRCA mutation carriers. N Engl J Med, 2009. 361(2): p. 123-34.]. There were minimal adverse events (AEs) in these particular patients and there was no increase in the frequency of AEs in BRCA carriers compared to that in noncarriers. Subsequent proof-of-concept phase II trials in ovarian and breast cancer patients confirmed the responses as well as the low side effect profile of olaparib in this group of BRCA mutant cancer patients [Audeh M W, Carmichael J, Penson R T, et al., Oral poly(ADP-ribose) polymerase inhibitor olaparib in patients with BRCA1 or BRCA2 mutations and recurrent ovarian cancer: a proof-of-concept trial. Lancet, 2010. 376(9737): p. 245-51; Tuft A, Robson M, Garber J E, et al., Oral poly(ADP-ribose) polymerase inhibitor olaparib in patients with BRCA1 or BRCA2 mutations and advanced breast cancer: a proof-of-concept trial. Lancet, 2010. 376(9737): p. 235-44.]
Interestingly, response of ovarian cancer patients carrying BRCA1/2 mutations to PARP inhibitors was associated with their sensitivity to prior platinum treatment [Fong P C, Yap T A, Boss D S, et al., Poly(ADP)-ribose polymerase inhibition: frequent durable responses in BRCA carrier ovarian cancer correlating with platinum-free interval. J Clin Oncol, 2010. 28(15): p. 2512-9.]. Similar correlation with platinum-sensitivity was also seen in high-grade serous ovarian cancer patients without BRCA mutations [Gelmon K A, Tischkowitz M, Mackay H, et al., Olaparib in patients with recurrent high-grade serous or poorly differentiated ovarian carcinoma or triple-negative breast cancer: a phase 2, multicentre, open-label, non-randomised study. Lancet Oncol, 2011. 12(9): p. 852-61.]. Another phase II clinical study has shown that olaparib as maintenance therapy was beneficial in patients with relapsed, high-grade serous ovarian cancer, who were sensitive to platinum [Ledermann J, Harter P, Gourley C, et al., Olaparib maintenance therapy in platinum-sensitive relapsed ovarian cancer. N Engl J Med, 2012. 366(15): p. 1382-92.]. Based on these data, phase III registration trials have been initiated for olaparib in breast and ovarian cancer patients.
In a recent phase II study, olaparib demonstrated good clinical activity when given in combination with paclitaxel in patients with recurrent and metastatic gastric cancer who progressed following first-line therapy [Bang Y-J, Im S-A, Lee K-W, et al., Olaparib plus paclitaxel in patients with recurrent or metastatic gastric cancer: A randomized, double-blind phase II study. J Clin Oncol, 2013. 31(suppl; abstr 4013).]. Eligible patients were stratified by their ataxia-telangiectasia mutated (ATM) status. Paclitaxel/olaparib combination extended patient's overall survival (OS) compared to paclitaxel single agent, especially in ATM-low sub-group. ATM is a serine/threonine protein kinase that plays a critical role in DNA damage induced signalling and the initiation of cell cycle checkpoint in response to DNA-damaging agents such as ionizing radiation [Stracker T H, Roig I, Knobel P A, et al., The ATM signaling network in development and disease. Front Genet, 2013. 4: p. 37.].
On Dec. 19, 2014, the U.S. Food and Drug Administration approved olaparib capsules (Lynparza, AstraZeneca Pharmaceuticals LP) as monotherapy for the treatment of patients with deleterious or suspected deleterious germline BRCA mutated (gBRCAm) (as detected by an FDA-approved test) advanced ovarian cancer who have been treated with three or more prior lines of chemotherapy. Concurrent with this action, FDA approved the BRACAnalysis CDx (Myriad Genetics) for the qualitative detection and classification of variants in the BRCA1 and BRCA2 genes.
There are several other investigational PARP inhibitors in the clinic, including veliparib (ABT-888; Abbott Laboratories), rucaparib (AG014669; Clovis), niraparib (MK-4827; Tesaro), BMN-673 (Biomarin), CEP-9722 (Cephalon), and E7016 (Eisai). All these PARP inhibitors are different in their potency, selectivity, and DNA trapping activity. A recent report suggests that DNA trapping by PARP-inhibitor complex is one of the major mechanisms by which PARP inhibitors induce cytotoxicity in cells [Murai J, Huang S Y, Das B B, et al., Trapping of PARP1 and PARP2 by Clinical PARP Inhibitors. Cancer Res, 2012. 72(21): p. 5588-99.]. Veliparib is a potent PARP1/2 inhibitor but with weak DNA trapping activity and cellular cytotoxicity in BRCA mutant cells. Most of its clinical development has been focused on combination with chemotherapeutics. Recently, it was shown in a phase II trial that adding combination of veliparib plus carboplatin to standard neoadjuvant chemotherapy improved outcomes for women with triple-negative breast cancer [Rugo H, Olopade O, DeMichele A, et al., Veliparib/carboplatin plus standard neoadjuvant therapy for high-risk breast cancer: First efficacy results from the I-SPY 2 TRIAL. 2013. Abstract S5-02.]. For rucaparib, niraparib, and BMN-673, monotherapy has demonstrated good clinical activity in BRCA mutant cancer patients [Shapiro G, Kristeleit R, Middleton M, et al., Pharmacokinetics of orally administered rucaparib in patients with advanced solid tumors. Mol Cancer Ther, 2013. 12(11 Suppl): Abstract nr A218; Michie C O, Sandhu S K, Schelman W R, et al., Final results of the phase I trial of niraparib (MK4827), a poly(ADP)ribose polymerase (PARP) inhibitor incorporating proof of concept biomarker studies and expansion cohorts involving BRCA1/2 mutation carriers, sporadic ovarian, and castration resistant prostate cancer (CRPC). J Clin Oncol, 2013. 31(suppl; abstr 2513); Bono J S D, Mina L A, Gonzalez M, et al., First-in-human trial of novel oral PARP inhibitor BMN 673 in patients with solid tumors. J Clin Oncol, 2013. 31(suppl; abstr 2580)].
Phase III trials for these PARP inhibitors are currently underway in breast and/or ovarian cancer patients with BRCA mutation or platinum sensitive disease.
(R)-2-fluoro-10a-methyl-7,8,9,10,10a,11-hexahydro-5,6,7a,11-tetraazacyclohepta[def]cyclopenta[a]fluoren-4(5H)-one (or “Compound A”) is a highly selective PARP1/2 inhibitor. Compound A potently inhibits intracellular PARP activity and specifically inhibits the proliferation of cell lines with BRCA1/2 mutations or other HR deficiencies. Compound A significantly induces tumor regression in BRCA1 mutation breast cancer xenograft model at much lower dose than olaparib. Compound A has excellent DMPK properties and significant brain penetration.
Data generated in preclinical biochemical, cell-based and animal studies suggest that Compound A could offer significant patient benefit in inhibiting tumors harboring BRCA gene mutations or homologous recombination defects. It has good brain penetration and might show activity in more indication such as glioblastoma. These unique characteristics warrant further evaluation of Compound A in clinical studies.
The free base, i.e., (R)-2-fluoro-10a-methyl-7,8,9,10,10a,11-hexahydro-5,6,7a,11-tetraazacyclohepta[def]cyclopenta[a]fluoren-4(5H)-one (or “Compound A”) has been disclosed as a highly selective and potent Parp1/2 inhibitor, See WO 2013/097225 A1 which is incorporated herein by reference.

Compound A is a multiple ring-fused complex molecule with a quarterly chiral center. Compound A in a free base form was obtained originally through “chiral pool” method which was extremely inefficient and difficult for scale-up because multiple chromatography columns were needed for the purification of the intermediates and the final product. In addition, Compound A prepared in such a way has unsatisfactory optical purity because the partial racemization occurred during manufacturing process (although the underlining reasons remain uncertain). Therefore, there is a great need for a process suitable for large-scale preparation of Compound A (especially crystalline forms thereof) with reproducibility and good quality for formulation development.